62 research outputs found
Optical and radio properties of extragalactic radio sources with recurrent jet activity
We present a sample of 74 radio sources with recurrent jet activity. The
sample consists of 67 galaxies, 2 quasars and 5 unidentified sources, selected
from the published data or are newly recognized. The sample's redshift range is
0.002 < z < 0.7 and the size of inner and outer structures varies from 0.02 to
4248 kpc. We analyse the optical and radio properties of the sample and compare
them with the characteristics of ordinary one-off FRII radio sources. With the
help of stellar population modelling, we derive black hole masses and stellar
masses of host galaxies of 35 restarting radio sources, finding that the black
hole masses in restarting radio sources are comparable to those of typical
single-cycle FRII radio sources. The obtained median values of log M are
8.58 and 8.62 M Unlike the black hole masses, the stellar masses in
restarting radio sources tend to be smaller than in the FRII sources. Although
the stellar populations of the hosts of recurrent activity sources are
dominated by old stars, a significant fraction of young stars can be observed
as well. Based on the Sloan Digital Sky Survey photometric observations, we
also analyse the morphology of the host galaxies and obtained significantly
smaller concentration indices for the restarting radio sources when compared to
the classical FRII hosts. This effect can be interpreted as a result of
frequent merger events in the history of host galaxies of restarting radio
sources.Comment: 21 pages, 17 figure
Catalogue with visual morphological classification of 32,616 radio galaxies with optical hosts
We present the catalogue of Radio sources associated with Optical Galaxies
and having Unresolved or Extended morphologies I (ROGUE I). It was generated by
cross-matching galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS
DR 7) as well as radio sources from the First Images of Radio Sky at Twenty
Centimetre (FIRST) and the National Radio Astronomical Observatory VLA Sky
Survey (NVSS) catalogues. We created the largest handmade catalogue of visually
classified radio objects and associated with them optical host galaxies,
containing 32,616 galaxies with a FIRST core within 3 arcsec of the optical
position. All listed objects possess the good quality SDSS DR 7 spectra with
the signal-to-noise ratio 10 and spectroscopic redshifts up to . The
radio morphology classification was performed by a visual examination of the
FIRST and the NVSS contour maps overlaid on a DSS image, while an optical
morphology classification was based on the 120 arcsec snapshot images from SDSS
DR 7.
The majority of radio galaxies in ROGUE I, i.e. 93%, are unresolved
(compact or elongated), while the rest of them exhibit extended morphologies,
such as Fanaroff-Riley (FR) type I, II, and hybrid, wide-angle tail,
narrow-angle tail, head-tail sources, and sources with intermittent or
reoriented jet activity, i.e. double-double, X-shaped, and Z-shaped. Most of FR
IIs have low radio luminosities, comparable to the luminosities of FR Is.
Moreover, due to visual check of all radio maps and optical images, we were
able to discover or reclassify a number of radio objects as giant,
double-double, X-shaped, and Z-shaped radio galaxies. The presented sample can
serve as a database for training automatic methods of identification and
classification of optical and radio galaxies.Comment: Proceedings paper under the IAU symposium "Nuclear Activity in
Galaxies Across Cosmic Time", eds. M. Povic, P. Marziani, J. Masegosa, H.
Netzer, S. H. Negu, and S. B. Tessem
Constraining jet production scenarios by studies of Narrow-Line-Radio-Galaxies
We study a large sample of narrow-line radio galaxies (NLRGs) with extended
radio structures. Using 1.4 GHz radio luminosities, , narrow optical
emission line luminosities, L_{\oiii} and , as well as black
hole masses derived from stellar velocity dispersions measured from
the optical spectra obtained with the Sloan Digital Sky Survey, we find that:
(i) NLRGs cover about 4 decades of the Eddington ratio, ; (ii) strongly
correlates with ; (iii) radio-loudness, , strongly anti-correlates with . A very broad range
of the Eddington ratio indicates that the parent population of NLRGs includes
both radio-loud quasars (RLQs) and broad-line radio galaxies (BLRGs). The
correlations they obey and their high jet production efficiencies favor a jet
production model which involves the so-called 'magnetically choked' accretion
scenario. In this model, production of the jet is dominated by the
Blandford-Znajek mechanism, and the magnetic fields in the vicinity of the
central black hole are confined by the ram pressure of the accretion flow.
Since large net magnetic flux accumulated in central regions of the accretion
flow required by the model can take place only via geometrically thick
accretion, we speculate that the massive, 'cold' accretion events associated
with luminous emission-line AGN can be accompanied by an efficient jet
production only if preceded by a hot, very sub-Eddington accretion phase.Comment: 24 pages, 6 figures, published in ApJ, moderate revisions to match
the published versio
On the diversity of the jet production efficiency in Swift/BAT AGNs
We address the very large diversity of the jet production efficiency in
active galactic nuclei (AGNs) by using data on low redshift AGNs selected from
the Swift/BAT catalog and having black hole (BH) masses larger than
. Most of these AGNs accrete at intermediate rates and
have bolometric luminosities dominated by mid-IR radiation. Our sample contains
radio-loud (RL), radio-intermediate (RI), and radio-quiet
(RQ) AGNs. All RL objects are found to have extended radio structures and most
of them have classical FR II morphology. Converting their radio loudness to the
jet production efficiency, we find that the median of this efficiency is on the
order of , where is the
radiation efficiency of the accretion disk. Without knowing the contribution of
jets to the radio emission in the RQ AGNs, we are only able to estimate their
efficiencies using upper limits. Their median is found to be
. Our results suggest that some threshold conditions
must be satisfied to allow production of strong, relativistic jets in RL AGNs.
We discuss several possible scenarios and argue that the production of
collimated, relativistic jets must involve the Blandford-Znajek mechanism and
can be activated only in those AGNs whose lifetime is longer than the time
required to enter the magnetically arrested disk (MAD). Presuming that MAD is
required to collimate relativistic jets, we expect that the weak
nonrelativistic jets observed in some RQ AGNs are produced by accretion disks
rather than by rotating BHs.Comment: 18 pages, 4 figures. Published in ApJ on 2020 September
Period changes of the sample of eclipsing binaries with active chromospheres
In this work we present results derived from analysis of the O-C behaviour of ten eclipsing binary systems: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. It was proved on the basis of moments of minima compiled from the literature and new ones determined from recent observations, that these binaries show long term (19-91 years) modulations of their orbital periods, clearly visible in their O-C diagrams. Two possible explanations for this effect are considered: (1) the light-travel time effect due to the presence of a third body orbiting the eclipsing systems; (2) the Applegate mechanism predicting period modulation by changes in the distribution of angular momentum as a star goes through its activity cycles. It was found that in the case of four systems the existence of a third star, orbiting the binary, is a more plausible explanation of observations
Multiwavelength variability of the radio quasar J2042+7508
In this paper, we present our results of study on the long term multiwavelength variability properties of the quasar J2042+7508 (4C +74.26) – a giant radio source located at the redshift of 0.104. This source exhibits interesting emission and structural properties when observed in various wavelengths, including X-ray, optical and radio frequencies. Therefore, exploring these properties through multifrequency variability studies presents a great importance to our understanding of the evolution of quasars and radio-loud unification schemes. We found a trend of anticorrelation with time lag of about three months between optical and radio light curves. A weak correlation with a longer time lag of about 230 days might also exist. Using the structure function method, applied to our six years long, optical data, we arrived at a conclusion that the quasar variability with amplitude of about 0.3 magnitude, is likely caused by an accretion disk instability
Caltech-NRAO Stripe 82 Survey (CNSS) Paper V: AGNs that transitioned toradio-loud state
A recent multi-year Caltech-NRAO Stripe 82 Survey (CNSS) revealed a group of objects that appeared as new radio sources after >5--20 years of absence. They are transient phenomena with respect to the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and constitute the first unbiased sample of renewed radio activity. Here we present the follow-up, radio, optical and X-ray study of them. The group consist of 12 sources, both quasars and galaxies with wide redshift (0.04 24.5) distribution. Their radio properties in the first phase of activity, namely the convex spectra and compact morphology, allow them all to be classified as gigahertz-peaked spectrum (GPS) sources. We conclude that the spectral changes are a consequence of the evolution of newly-born radio jets. Our observations show that over the next few years of activity the GPS galaxies keep the convex shape of the spectrum, while GPS quasars rapidly transform into flat-spectrum sources, which may result in them not being recognized as young sources. The wide range of bolometric luminosities, black hole masses and jet powers among the transient sources indicates even greater population diversity in the group of young radio objects. We also suggest that small changes of the accretion disc luminosity (accretion rate) may be sufficient to ignite low-power radio activity that evolves on the scale of decades
J1420--0545: The radio galaxy larger than 3C236
We report the discovery of the largest giant radio galaxy, J1420-0545: a FR
type II radio source with an angular size of 17.4' identified with an optical
galaxy at z=0.3067. Thus, the projected linear size of the radio structure is
4.69 Mpc (if we assume that H_{0}=71 km\s\Mpc, Omega_{m}=0.27, and
Omega_{\Lambda}=0.73). This makes it larger than 3C236, which is the largest
double radio source known to date. New radio observations with the 100 m
Effelsberg telescope and the Giant Metrewave Radio Telescope, as well as
optical identification with a host galaxy and its optical spectroscopy with the
William Herschel Telescope are reported. The spectrum of J1420-0545 is typical
of elliptical galaxies in which continuum emission with the characteristic
4000A discontinuity and the H and K absorption lines are dominated by evolved
stars. The dynamical age of the source, its jets' power, the energy density,
and the equipartition magnetic field are calculated and compared with the
corresponding parameters of other giant and normal-sized radio galaxies from a
comparison sample. The source is characterized by the exceptionally low density
of the surrounding IGM and an unexpectedly high expansion speed of the source
along the jet axis. All of these may suggest a large inhomogeneity of the IGM.Comment: 20 pages, 5 figures, 3 table
Optical monitoring of FRII-type radio quasars
We present preliminary results of optical monitoring of sample of FRII-type radio quasars. The optical observations were made with three telescopes, among them one robotic, spanning a time interval longer than two years. Variability in the range of a fraction of a magnitude was observed for all eight targets. We applied the structure function to analyse the brightness changes. The slope of the structure function is only consistent with the disk instability model for two sources; the other sources show values between of the disk instability and starburst models. Finally we argue that such monitoring would be most suitable as a long-term, complementary program for robotic telescopes
CGCG 292-057 - a radio galaxy with merger-modulated radio activity
We announce the discovery of a unique combination of features in a radio
source identified with the merger galaxy CGCG 292-057. The radio galaxy both
exhibits a highly complex, X-like structure and shows signs of recurrent
activity in the form of double-double morphology. The outer lobes of CGCG
292-057 are characterized by low radio power, P_{1400MHz} \simeq 2 * 10^{24}
W\Hz^{-1}, placing this source below the FRII/FRI luminosity threshold, and are
highly polarized (almost 20 per cent at 1400 MHz) as is typical of X-shaped
radio sources. The host is a LINER-type galaxy with a relatively low black hole
mass and double-peaked narrow emission lines.
These features make this galaxy a primary target for studies of
merger-triggered radio activity.Comment: 7 pages, 5 figures, submitted to MNRA
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